The invention relates to a paper sack, preferably a valve paper sack, for bulk material such as cement, gypsum, granulate, animal feed or similar, having a base, preferably a cross bottom or block bottom, and having an upper part which is disposed opposite the base and in which a valve hose is optionally arranged for filling the paper sack.
Such paper sacks are known, for example, from EP 1 858 759 B1. The typical sizes 5 kg, 10 kg or 25 kg are in particular commercially widespread. They have one or more paper layers which are formed from paper or from a paper composite and/or from coated paper.
A valve hose is optionally provided for filling such sacks which is worked into the upper part and which is placed onto a filler nozzle for filling. A fast escaping of the air during the filling process is of material significance for a fast and economic filling. On the other hand, the sack should be as leakproof as possible after the filling. To achieve a greater product protection or a longer product stability of the filling material, a barrier layer can—as described in EP 1 858 769 B1—be interposed between an inner layer and an outer layer of paper.
It has been found that a sufficient product protection cannot be ensured with the already known sacks with sensitive filling materials. Such sensitive filling materials are, for example, fast-binding products in the sector of construction materials or foodstuffs in which a loss of aroma has to be prevented.
It has been found to be disadvantageous with already known sacks inter alia that the barrier layer was only interposed loosely overlapping so that a sufficient product protection was not possible or the product stability of the filling material was not sufficiently long. In addition, sack solutions have been found to be disadvantageous in which a further paper layer is arranged within the barrier layer because the residual moisture contained in the paper can diffuse into the filling material and thereby causes the latter to age faster or destroys it.